Influenza Treatment Guidelines

Introduction to Influenza Treatment

• The Centers for Disease Control and Prevention (CDC) and the American Academy of Pediatrics (AAP) recommend neuraminidase inhibitors (oseltamivir or zanamivir) as the first-line treatment for H3N2 influenza, with treatment ideally initiated within 48 hours of symptom onset to maximize effectiveness 1, 2
• The American Academy of Family Physicians also supports the use of neuraminidase inhibitors as first-line treatment for influenza 3, 4, 5, 6

First-Line Treatment

• The dosage for patients ≥7 years is 10 mg (2 inhalations) twice daily for 5 days 1
• Oseltamivir reduces the duration of uncomplicated influenza illness by approximately 1 day compared to placebo, and may reduce risk of pneumonia by approximately 50% among influenza-infected patients, as recommended by the CDC and the American Academy of Family Physicians 3, 4, 5, 6
• Oseltamivir may reduce hospital admissions, particularly in high-risk patients, and reduces risk of secondary complications such as otitis media in children, supported by the CDC and the AAP 3, 7, 8, 9

Treatment Prioritization

• Treatment should be prioritized for patients with severe, complicated, or progressive illness requiring hospitalization, as well as high-risk patients with suspected or confirmed influenza, including adults ≥65 years, children <2 years, pregnant or postpartum women, and individuals with chronic medical conditions 1, 2
• Infants with congenital heart disease are considered high-risk for influenza complications, making antiviral treatment particularly important, supported by the CDC and the AAP 10, 11

Optimal Timing and Clinical Benefit

• The American Academy of Pediatrics and the CDC recommend that treatment should begin within 48 hours of symptom onset for maximum effectiveness, reducing the duration of symptoms by approximately 1 day in uncomplicated cases 1
• Late treatment may still be beneficial for hospitalized patients or those with severe illness even if started >48 hours after symptom onset 1
• The efficacy of antiviral medications decreases significantly if treatment is initiated more than 48 hours after the onset of symptoms, as recommended by the CDC 12

Resistance and Antibacterial Therapy

• Current H3N2 strains are resistant to adamantanes (amantadine and rimantadine), so these drugs should not be used 1, 13
• Antibacterial therapy should target likely pathogens such as S. pneumoniae, S. pyogenes, and S. aureus (including MRSA) 1
• For patients with severe influenza-related pneumonia, combination therapy with antibiotics is recommended, with a preferred regimen of broad-spectrum β-lactamase stable antibiotic (co-amoxiclav or cephalosporin) plus a macrolide, according to the Journal of Infection and the CDC 14

Dosage and Administration

• The following table outlines the treatment dosage for oseltamivir based on weight:

• For term infants:

  Age	Dosage
  0-8 months	3 mg/kg twice daily for 5 days
  9-11 months	3.5 mg/kg twice daily for 5 days [15, 16, 17]

• For preterm infants, the recommended dosage is 1.0 mg/kg twice a day for those less than 38 weeks postmenstrual age, 1.5 mg/kg twice a day for those 38-40 weeks postmenstrual age, and 3.0 mg/kg twice a day for those more than 40 weeks postmenstrual age, according to the Pediatrics society 11
• For patients with moderate renal insufficiency (creatinine clearance 10-30 mL/min), the recommended treatment dosage is 75 mg once a day for 5 days, and the recommended prophylaxis dosage is 30 mg once a day or 75 mg every two days for 10 days, as suggested by the Pediatrics society, the CDC, and the AAP 10, 2, 13

Alternative Treatments

• Zanamivir is 84% effective in preventing febrile, laboratory-confirmed influenza illness, with a mechanism as a neuraminidase inhibitor, and is administered via inhaled powder via Diskhaler device, with a dosage of 10 mg (two 5 mg inhalations) twice daily for 5 days, as recommended by the CDC 1, 18
• Baloxavir is a cap-dependent endonuclease inhibitor with a single oral dose, and weight-based dosing (40-80 mg once), offering a single-dose treatment with improved compliance, effective against both influenza A and B, supported by the CDC and the Infectious Diseases Society of America (IDSA) 7, 19
• Amantadine is an M2 ion channel inhibitor, with an efficacy of 70-90% in preventing illness from influenza A, administered orally, with a dosage of 100 mg twice daily for 5 days, but only effective against influenza A and has high rates of resistance in circulating strains, as reported by the CDC and the IDSA 7, 19
• Rimantadine is also an M2 ion channel inhibitor, with an efficacy of 70-90% in preventing illness from influenza A, administered orally, with a dosage of 100 mg twice daily for 5 days, but only effective against influenza A, with high rates of resistance in circulating strains, and less CNS side effects than amantadine, supported by the CDC and the IDSA 7, 19

Special Populations

• Antiviral medications can be used in patients with solid organ transplants, regardless of the duration of symptoms, as recommended by the CDC 8
• Oseltamivir can be used safely in recipients of hematopoietic stem cell transplants, according to the American Society of Transplantation 2
• Immunocompromised patients may benefit from antiviral treatment even if started >48 hours after symptom onset, and may require longer treatment duration, according to the CDC and the MMWR Recommendations and Reports 1, 18
• The use of antiviral medications during pregnancy should be evaluated on a case-by-case basis, as the benefit may outweigh the risk in cases of severe influenza, according to the AAP 16
• The use of antiviral medications during breastfeeding should be evaluated on a case-by-case basis, with consideration of the risk-benefit ratio, as recommended by the AAP 16

Adverse Effects and Contraindications

• The most common adverse effects of oseltamivir are gastrointestinal, including nausea in up to 10% and vomiting in approximately 9% of adults, according to the CDC 20
• Taking oseltamivir with food may improve gastrointestinal tolerability, as suggested by the American Academy of Pediatrics 11
• Patients with a history of seizures should use antiviral medications with caution, although there are no epidemiological studies that report an increased risk, as noted by the CDC 2
• Antiviral medications for influenza (oseltamivir, zanamivir, and peramivir) are contraindicated in patients with known hypersensitivity to the medication, and zanamivir is specifically contraindicated in patients with underlying respiratory disease such as asthma or COPD due to the risk of potentially fatal bronchospasm, as recommended by the CDC and the AAP 2, 15

Common Mistakes in Influenza Treatment

• Delayed initiation of treatment, inappropriate selection of antiviral agents, overuse of antibiotics, inadequate duration of treatment, and forgetting prophylaxis are common mistakes in influenza treatment, which can reduce effectiveness and increase the risk of complications, as reported by the CDC, the AAP, and the IDSA 1, 18, 14